This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 11(1999)-90050 filed on Mar. 30, 1999, the entire content of which is incorporated herein by reference.
The present invention generally relates to vehicle braking devices or clutch devices. More particularly, the present invention pertains to a master cylinder for use in association with a braking device or a clutch device of an automotive vehicle.
Japanese Patent Laid-Open Publication No. Hei. 10-297463 published in 1998 without examination describes a master cylinder that includes a cylinder body in which is formed a cylinder bore, and a piston fitted in the cylinder bore for back and forth movement. The piston defines a pressure chamber in the cylinder bore at the front side of the piston. The piston is configured to be of a fixed diameter and so the input/output characteristics of the master cylinder is constant or remains unchanged.
However, recently, from the view point of safety during vehicle driving or cruising, it is desirable that the brake system of an automotive vehicle be capable of being controlled in various high precision ways. There is thus a need for a master cylinder having varied input/output characteristics.
According to one aspect of the invention, a master cylinder is designed to provide variable input/output characteristics. The master cylinder includes a body in which is formed a bore, and a piston fitted in the cylinder bore and movable upon brake operation. The piston is divided into a front portion and a rear portion, with a pressure chamber being defined at the front side of the front portion and an auxiliary chamber being defined at the rear side of the front portion. The auxiliary pressure chamber is located at the same position as the rear portion of the piston. A first changeover valve is provided between the auxiliary pressure chamber and the pressure chamber to establish and interrupt fluid communication between the auxiliary pressure chamber and the pressure chamber.
Preferably, the front portion of the piston is larger in diameter than the rear portion of the piston so that the master cylinder provides a larger output when the auxiliary pressure chamber is in fluid communication with the pressure chamber than when the auxiliary pressure chamber is out of fluid communication with the pressure chamber subject to the same inputs to the master cylinder. Also, the front portion of the piston is movable relative to the rear portion of the piston.
A pressure increasing mechanism is provided for increasing the pressure in the auxiliary pressure chamber. The pressure increasing mechanism advantageously increases the pressure of the brake fluid in the auxiliary pressure chamber, which causes the piston to move in the frontward direction, thereby increasing the pressure of the brake fluid in the pressure chamber. A second changeover valve is provided for establishing and interrupting fluid communication between the auxiliary pressure chamber and a reservoir supplying brake fluid to the auxiliary pressure chamber. The pressure increasing mechanism, the first changeover valve, and the second changeover valve are preferably under the control of a common control device. Further, the piston is provided with a communication passage thorough which the pressure chamber is in fluid communication with a main reservoir for supplying brake fluid to the pressure chamber. The communication passage is closed by a seal cup to interrupt fluid communication between the pressure chamber and the main reservoir when the piston moves through a distance relative to the cylinder body.
According to another aspect of the invention, a master cylinder includes a cylinder body in which is defined a bore, and a piston in the bore that is movable in response to brake operation. The piston includes a front portion and a rear portion, with the front portion being movable relative to the rear portion. A pressure chamber is defined within the bore on the front side of the front portion of the piston and an auxiliary pressure chamber is located at the rear side of the front portion of the piston. A communication passage connects the auxiliary pressure chamber to the pressure chamber.
In accordance with another aspect of the invention, a master cylinder includes a cylinder body possessing a bore and a piston positioned in the bore for movement within the bore. The piston includes a front portion and a rear portion, with the front portion being movable relative to the rear portion and having a larger diameter than the rear portion. A pressure chamber is located at the front side of the front portion of the piston and an auxiliary pressure chamber is located at the rear side of the front portion of the piston.